1. Field of the Invention
The present invention relates generally to a window for sealing a vacuum chamber and transmitting radiation or electrons.
2. Related Art
X-ray sources or x-ray detectors utilize a vacuum chamber with a window through which x-rays are transmitted. The window can be formed of beryllium foil that is typically made by rolling. The rolling can produce a mosaic of crystallites with grain boundaries that can leak gas. In the vacuum chamber, even minute amounts of gas pose a serious threat to the operation and longevity of x-ray detectors and x-ray emitters. Beryllium windows are typically made relatively thick (greater than about 23 μm) to prevent leaks. Unfortunately, the thickness of the window prevents transmission of the soft x-rays emitted by sodium and elements with even lower atomic numbers (Z). Thinner beryllium windows have proven difficult to attach to support structures without leaving leaks in the resulting assembly.
In addition, beryllium windows can develop leaks if its mounting promotes stress concentration. It has been proposed to relieve at least some of the stress concentration by mounting the beryllium window over a ring that retains its shape even when it is heated. The window can be subjected to heat during mounting or during use.
The beryllium window is typically brazed to a support structure to form a window assembly that can be attached to the vacuum chamber and processed at temperatures above 250 degrees Celsius. Brazing has proven effective for relatively thicker windows (greater than about 30 μm) windows, but not for beryllium windows thin enough to transmit the soft x-rays of interest.
An alternative is the use of an adhesive. Adhesives can still allow certain gases (e.g. oxygen) to diffuse through them when the vacuum chamber is evacuated. In addition, the window must still be thick enough to avoid leaks, and this thickness blocks the soft x-rays.